1. Field of the Invention
This invention relates to a method for adhesively joining pipes.
2. Description of the Prior Art
Pipes are currently joined by soldering, welding, threading, bonding with epoxy adhesives, bonding with polyvinylchloride adhesives in the case of PVC pipe, or using butts and straps. Threading, soldering and welding methods require skilled tradesmen and are therefor costly.
Epoxy adhesives are the bonding material of choice where the pipes are to be used to convey hot water or steam since they have the requisite chemical inertness and resistance to high temperatures. In addition, epoxy adhesives are particularly useful to join pipes of diverse materials. Adhesiveness may vary significantly from material to material with particular adhesives. Thus, an adhesive which is satisfactory for bonding steel may be inadequate for bonding a glass fiber reinforced resin. Epoxy adhesives have good adhesiveness with a broad range of materials and thus are extremely useful in bonding pipes having different compositions. As used, the epoxy adhesive comprises a two package composition which is mixed together prior to coating. The pot life of the mixed adhesive is short, being less than 30 minutes. After the pipe ends are coated and joined together the joints are heated, as by heating blankets, to accelerate the cure. Depending on the size of the joint, this takes from 10 to 60 minutes. During the heating step the epoxy adhesive becomes very fluid prior to cure. As a result, the adhesive flows out of the joint to form "icicles" which eventually harden and impede the flow of fluid through the pipe. As much as 75% of a pipe opening can be closed off due to the formation of "icicles" in this manner, and increased pumping costs and reduced efficiency of the piping system are the inevitable result. Also, because of the limited pot life of the epoxy adhesives when working with large diameter pipes, i.e., 6-12 inches, it is difficult to completely seal the surface before the adhesive sets up.